1. Field of the Invention
The present invention is directed to integrating optics on the wafer level, particularly for realizing a high numerical aperture system.
2. Description of Related Art
Magneto-optical heads are used to read current high-density magneto-optic media. In particular, a magnetic coil is used to apply a magnetic field to the media and light is then also delivered to the media to write to the media. The light is also used to read from the media in accordance with the altered characteristics of the media from the application of the magnetic field and light.
An example of such a configuration is shown in FIG. 1. In FIG. 1, an optical fiber 8 delivers light to the head. The head includes a slider block 10 which has an objective lens 12 mounted on a side thereof. A mirror 9, also mounted on the side of the slider block 10, directs light from the optical fiber 8 onto the objective lens 12. A magnetic coil 14, aligned with the lens 12, is also mounted on the side of the slider block 10. The head sits on top of an air bearing sandwich 16 which is between the head and the media 18. The slider block 10 allows the head to slide across the media 18 and read from or write to the media 18.
The height of the slider block 10 is limited, typically to between 500-1500 microns, and is desirably as small as possible. Therefore, the number of lenses which could be mounted on the slider block is also limited. Additionally, alignment of more than one lens on the slider block is difficult. Further, due to the small spot required, the optics or overall optical system of the head need to have a high numerical aperture, preferably greater than 0.6. This is difficult to achieve in a single objective lens due to the large sag associated therewith. The overall head is thus difficult to assemble and not readily suited to mass production.
Therefore, it is an object of the present invention to provide an integrated optical system that substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is another object of the present invention to integrating optics on the wafer level to create a high numerical aperture system.
The above and other objects of the present invention may be realized by providing an integrated micro-optical apparatus including a die formed from more than one wafer bonded together, each wafer having a top surface and a bottom surface, bonded wafers being diced to yield multiple die, at least two optical elements being formed on respective surfaces of each die, at least one of said at least two optical elements being a spherical lens, a resulting optical system of each die having a high numerical aperture. The die may further include a compensating element which compensates for aberrations exhibited by the spherical lens. The compensating element may be on a surface immediately adjacent the spherical lens. The compensating element may be a diffractive element or an aspheric lens. The die may include at least one additional refractive element, all refractive elements of the die being formed in material having a high numerical aperture. The refractive element may be on a bottom wafer and of a material having a higher refractive index than that of the bottom wafer. The spherical lens may be made of a material having a higher index of refraction than a wafer on which it is formed, e.g., photoresist.
The die may include an aperture holding the spherical lens. The spherical lens in the aperture may be a ball lens. The ball lens may have a round spherical surface and a non-spherical surface. The non-spherical surface may be flat.
The bottom surface of the bottom wafer of the more than one wafer bonded together may include a layer of material deposited thereon. The layer of material may be deposited in accordance with a difference between a desired thickness and a measured thickness of the die. The layer may have a different refractive index than said bottom wafer. The spacing between wafers may be varied in accordance with a difference between a desired thickness of a wafer and a measured thickness of the wafer. The spacing may be varied in accordance with a difference between a desired thickness and a measured thickness of the die.
The above and other objects of the present invention may be realized by providing a method for forming an integrated micro-optical apparatus including bonding a first wafer and a second wafer together, each wafer having a top surface and a bottom surface; etching a plurality of holes in the first wafer, placing a round spherical lens in each of the holes of the first wafer, dicing bonded first and second wafers to yield multiple dies, and, before dicing, forming at least one optical element on one of the top surface and the bottom surface of the second wafer.
The method may further include modifying a surface of the round spherical lens to form a non-spherical surface. The non-spherical surface may be flat. The modifying may include polishing. The placing may include providing bonding material between said round spherical lens and the first wafer. The providing may include coating the round spherical lens in the hole with a wettable metal and then coating the round spherical lens in the hole with solder. The etching may include etching the first wafer from both the first and second surface of the first wafer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.